1. Field of the Invention
The present invention relates generally to equipment for the treatment of waste material and more particularly to anaerobic sludge digestion tank equipment utilizing a double membrane to maintain constant pressure in a variable volume region housing the gas produced during the anaerobic process.
2. Background of the Invention
The use of digestive tanks utilizing anaerobic treatment of waste water sludge is well known and practiced in the art. During the anaerobic process, gases, typically methane and carbon dioxide, are given off and collected to be used as the fuel for heating the sludge mixture. Many of the systems employ a floating gas holder positioned above the sludge which collects the gas and provides a controllable downward force on the gas, thus resulting in the gas being pressurized and immediately useable in the sludge heating equipment. The tank facilities must meet environmental limitations concerning the discharge of gases into the atmosphere and careful monitoring and control of the gases produced during the anaerobic process is essential since the gases frequently are explosive when intermixed with ambient atmospheric air. The floating gas holder while in theory is workable, is subject to corrosion and freezing, thus limiting its movement as well as tipping and gas leakages, all of which substantially interfere with its effective operation to properly control the gas within the tank. The optimum digestive tank would employ a system which would be capable of adapting to a changing volume of sludge mixture within the tank while still providing a constant pressure reservoir for the gas produced. Further, it is desirable that the system be capable of controlling the gases produced and hold them in a constant pressure environment while functioning without an external energy source over a reasonable period of time since the anaerobic process is not dependent upon external energy and would continue during periods of power outages and control of the system for the above stated reasons must be maintained.